Triaxial Model Research Articles

The Influence of Triaxiality Parameter γ on the Chiral Doublet Bands with (πg9/2)−1 (νh11/2)2 Configuration

The chiral doublet bands with three-quasiparticle configuration (πg9/2)−1 (νh11/2)2 are studied by the fully quantal triaxial particle rotor model. The energy spectra and B(M1)/B(E2) ratios of the doublet bands with different triaxiality parameter γ are systematically analyzed. It is found that γ is a sensitive parameter for the properties of these doublet bands.

A STELLAR DYNAMICAL MASS MEASUREMENT OF THE BLACK HOLE IN NGC 3998 FROM KECK ADAPTIVE OPTICS OBSERVATIONS

We present a new stellar dynamical mass measurement of the black hole in the nearby, S0 galaxy NGC 3998. By combining laser guide star adaptive optics observations obtained with the OH-Suppressing Infrared Imaging Spectrograph on the Keck II telescope with long-slit spectroscopy from the Hubble Space Telescope and the Keck I telescope, we map out the stellar kinematics on both small spatial scales, well within the black hole sphere of influence, and on large scales. We find that the galaxy is rapidly rotating and exhibits a sharp central peak in the velocity dispersion. Using the kinematics and the stellar luminosity density derived from imaging observations, we construct three-integral, orbit-based, triaxial stellar dynamical models. We find the black hole has a mass of M_BH = (8.1_{-1.9}^{+2.0}) x 10^8 M_sun, with an I-band stellar mass-to-light ratio of M/L = 5.0_{-0.4}^{+0.3} M_sun/L_sun (3-sigma uncertainties), and that the intrinsic shape of the galaxy is very round, but oblate. With the work presented here, NGC 3998 is now one of a very small number of galaxies for which both stellar and gas dynamical modeling have been used to measure the mass of the black hole. The stellar dynamical mass is nearly a factor of four larger than the previous gas dynamical black hole mass measurement. Given that this cross-check has so far only been attempted on a few galaxies with mixed results, carrying out similar studies in other objects is essential for quantifying the magnitude and distribution of the cosmic scatter in the black hole mass - host galaxy relations.

Shape Co-Existence in the Transitional Nuclide 157Yb

High-spin states in 157Yb have been populated in the 144Sm(16O, 3n)157Yb fusion-evaporation reaction at a beam energy of 85 MeV, and two rotational bands have been established for the first time. Within the framework of the triaxial particle-rotor model, the energy spectra and single-particle configurations of 157Yb are investigated. The calculated energy spectra agree well with the experimental data. The newly observed νf7/2 band, and the previously known νi13/2 band in 157Yb, are also discussed by means of Total-Routhian-Surface methods. The structural characters observed in 157Yb provide evidence for the shape coexistence of three distinct shapes: prolate, triaxial and oblate. At higher spins, both the νf7/2 band and the νi13/2 band in 157Yb undergo a shape evolution with sizable alignments occurring.

Models of cuspy triaxial stellar systems - I. Stability and chaoticity

We used the N-body code of Hernquist and Ostriker (1992) to build a dozen cuspy ({\gamma}\approx 1) triaxial models of stellar systems through dissipationless collapses of initially spherical distributions of 10^6 particles. We chose four sets of initial conditions that resulted in models morphologically resembling E2, E3, E4 and E5 galaxies, respectively. Within each set, three different seed numbers were selected for the random number generator used to create the initial conditions, so that the three models of each set are statistically equivalent. We checked the stability of our models using the values of their central densities and of their moments of inertia, which turned out to be very constant indeed. The changes of those values were all less than 3 per cent over one Hubble time and, moreover, we show that the most likely cause of those changes are relaxation effects in the numerical code. We computed the six Lyapunov exponents of nearly 5,000 orbits in each model in order to recognize regular, partially and fully chaotic orbits. All the models turned out to be highly chaotic, with less than 25 per cent of their orbits being regular. We conclude that it is quite possible to obtain cuspy triaxial stellar models that contain large fractions of chaotic orbits and are highly stable. The difficulty to build such models with the method of Schwarzschild (1979) should be attributed to the method itself and not to physical causes.

Effects of the Earth’ s triaxiality on the polar motion excitations

his study aims to evaluate the significance of the Earth’s triaxiality to the polar motion theory. First of all, we compare the polar motion theories for both the triaxial and rotationally-symmetric Earth models, which is established on the basis of the EGM2008 global gravity model and the MHB2000 Earth model. Then, we use the atmospheric and oceanic data (the NCEP/NCAR reanalyses and the ECCO assimulation products) to quantify the triaxiality effect on polar motion excitations. Numerical results imply that triaxiality only cause a small correction (about 0. 1–0.2 mas) to the geophysical excitations for the rotationally-symmetric case. The triaxiality correction is much smaller than the errors in the atmospheric and oceanic data, and thus can be neglected for recent studies on polar motion excitations.

The shapes and alignments of dark matter halos

We presentmeasurements of the triaxial dark matter halo shapes and alignment correlation functions in theMillennium and Millennium-2 dark matter N-body simulations. These two simulations allow us to measure the distributions of halo shapes down to 10% of the virial radius over a halo mass range of 6 × 109–2 × 1014 h−1M⊙. We largely confirm previous results on the distributions of halo axis ratios asa function of halo mass, but we find that the median angle between halo major axes at different halo radiican vary by a factor of 2 between the Millennium-1 and 2 simulations because of the different massresolution. Thus, error in the shape determinations from limited resolution is potentially degenerate with the misalignment of halo inner and outer shapes used to constrain Brightest Cluster Galaxy alignments in previous works.We also present simplifying parameterizations for the 3-D halo-mass alignment correlation functions that arenecessary ingredients for triaxial halo models of large-scale structure and models of galaxyintrinsic alignments as contaminants for cosmic shear surveys. We measure strong alignments between halos of all masses and the surroundingdark matter overdensities out to several tens of h−1 Mpc, in agreement with observed shear-galaxy and cluster shape correlations. We use these measurements to forecast the contribution to the weak lensing signal around galaxy clusters from correlated mass along the line-of-sight. For prolate clusters with major axes aligned with the line-of-sight the fraction of the weak lensing signal from mass external to the cluster can be twice that predicted if the excess halo alignment correlation is assumed to be zero.

Shape and motion estimate of LEO debris using light curves

We have derived a tri-axial ellipsoidal model of an LEO object, a Cosmos 2082 rocket body, including its rotational axis direction, rotation period, precession, and a compositional parameter, using only light curve data from an optical telescope. The brightness of the object was monitored for two days and least-squares fitting was used to determine these values. The derived axial ratios are 100:18:18, the coordinates of the rotational axis direction on the celestial sphere are R.A.=305.8° and Dec.=2.6°, and its observed average rotation period is 41s. When precession is considered, its amplitude and precession period are 30.5° and 29.4min. These results show that optical light curve data are sufficient to determine the shapes and the motions of LEO objects.

MORPHOLOGY OF GALAXY CLUSTERS: A COSMOLOGICAL MODEL-INDEPENDENT TEST OF THE COSMIC DISTANCE-DUALITY RELATION

Aiming at comparing different morphological models of galaxy clusters, we use two new methods to make a cosmological model-independent test of the distance-duality (DD) relation. The luminosity distances come from Union2 compilation of Supernovae Type Ia. The angular diameter distances are given by two cluster models (De Filippis et al. and Bonamente et al.). The advantage of our methods is that it can reduce statistical errors. Concerning the morphological hypotheses for cluster models, it is mainly focused on the comparison between elliptical $\beta$-model and spherical $\beta$-model. The spherical $\beta$-model is divided into two groups in terms of different reduction methods of angular diameter distances, i.e. conservative spherical $\beta$-model and corrected spherical $\beta$-model. Our results show that the DD relation is consistent with the elliptical $\beta$-model at $1\sigma$ confidence level (CL) for both methods, whereas for almost all spherical $\beta$-model parameterizations, the DD relation can only be accommodated at $3\sigma$ CL, particularly for the conservative spherical $\beta$-model. In order to minimize systematic uncertainties, we also apply the test to the overlap sample, i.e. the same set of clusters modeled by both De Filippis et al. and Bonamente et al.. It is found that the DD relation is compatible with the elliptically modeled overlap sample at $1\sigma$ CL, however for most of the parameterizations, the DD relation can not be accommodated even at $3\sigma$ CL for any of the two spherical $\beta$-models. Therefore it is reasonable that the marked triaxial ellipsoidal model is a better geometrical hypothesis describing the structure of the galaxy cluster compared with the spherical $\beta$-model if the DD relation is valid in cosmological observations.

Physical Simulation for Water Injection of Horizontal Wells in Naturally Fractured Buried- Hill Reservoirs

It is very complicated for the relationship between water injection and injection-production through horizontal well in a naturally fractured buried-hills reservoir. On the basis of simplifying and hypothesizing for the flowing equations of the dual medium, the mathematical model for fluid flowing in a reservoir is obtained, and 7 similarity principles is proposed also. To aim at simulating the practical development effect, with the direction of the similarity principle, the triaxial fluid physical models were formed. With this model, the physical simulations, such as different well deployment patterns for the horizontal wells, various well distance, various difference between injection and production, were all carried out, the oil-sweeping mechanics for the horizontal wells were analyzed. Thus, the optimum well deployment patterns, well distance, differential pressure between injection and production were all Fig. out, so that the research achievement can provide a technical foundation for the production with water-injection within horizontal wells in a naturally fractured buried-hill reservoir.

Weak lensing by triaxial galaxy clusters

Weak gravitational lensing studies of galaxy clusters often assume a spherical cluster model to simplify the analysis, but some recent studies have suggested this simplifying assumption may result in large biases in estimated cluster masses and concentration values, since clusters are expected to exhibit triaxiality. Several such analyses have, however, quoted expressions for the spatial derivatives of the lensing potential in triaxial models, which are open to misinterpretation. In this paper, we give a clear description of weak lensing by triaxial NFW galaxy clusters and also present an efficient and robust method to model these clusters and obtain parameter estimates. By considering four highly triaxial NFW galaxy clusters, we re-examine the impact of simplifying spherical assumptions and found that while the concentration estimates are largely unbiased except in one of our traixial NFW simulated clusters, for which the concentration is only slightly biased, the masses are significantly biased, by up to 40%, for all the clusters we analysed. Moreover, we find that such assumptions can lead to the erroneous conclusion that some substructure is present in the galaxy clusters or, even worse, that multiple galaxy clusters are present in the field. Our cluster fitting method also allows one to answer the question of whether a given cluster exhibits triaxiality or a simple spherical model is good enough.

Chiral Doublet Bands with νh11/2 ⊗ νd−15/2 Configuration in the Particle Rotor Model

Doublet bands with νh11/2⊗νd−15/2 configuration are studied for the first time via the triaxial particle rotor model. The main properties of the doublet bands, including the energy spectra and the electromagnetic transitions, are presented for different triaxiality parameter γ. The aplanar rotation and chiral geometry are discussed based on the analysis of angular momentum components.

Chaotic mixing and the secular evolution of triaxial cuspy galaxy models built with Schwarzschild’s method

We use both N-body simulations and integration in fixed potentials to explore the stability and the long-term secular evolution of self-consistent, equilibrium, non-rotating, triaxial spheroidal galactic models. More specifically, we consider Dehnen models built with the Schwarzschild method. We show that short-term stability depends on the degree of velocity anisotropy (radially anisotropic models are subject to rapid development of radial-orbit instability). Long-term stability, on the other hand, depends mainly on the properties of the potential, and in particular, on whether it admits a substantial fraction of strongly chaotic orbits. We show that in the case of a weak density cusp (gamma=1 Dehnen model) the N-body model is remarkably stable, while the strong-cusp (gamma=2) model exhibits substantial evolution of shape away from triaxiality, which we attribute to the effect of chaotic diffusion of orbits. The different behaviour of these two cases originates from the different phase space structure of the potential; in the weak-cusp case there exist numerous resonant orbit families that impede chaotic diffusion. We also find that it is hardly possible to affect the rate of this evolution by altering the fraction of chaotic orbits in the Schwarzschild model, which is explained by the fact that the chaotic properties of an orbit are not preserved by the N-body evolution. There are, however, parameters in Schwarzschild modelling that do affect the stability of an N-body model, so we discuss the recipes how to build a `good' Schwarzschild model.

Triaxial shapes in the interacting vector boson model

A new dynamical symmetry limit of the two-fluid interacting vector boson model (IVBM), defined through the chain $\text{Sp}(12,R)\ensuremath{\supset}\text{U}(3,3)\ensuremath{\supset}{\text{U}}^{*}(3)\ensuremath{\bigotimes}\text{SU}(1,1)\ensuremath{\supset}{\text{SU}}^{*}(3)\ensuremath{\supset}\text{SO}(3)$, is introduced. The SU${}^{*}$(3) algebra considered in the present paper closely resembles many properties of the SU${}^{*}$(3) limit of the interacting boson model-2, which have been shown by many authors geometrically to correspond to the rigid triaxial model. The influence of different types of perturbations on the SU${}^{*}$(3) energy surface, in particular the addition of a Majorana interaction and an O(6) term to the model Hamiltonian, is studied. The effect of these perturbations results in the formation of a stable triaxial minimum in the energy surface of the IVBM Hamiltonian under consideration. Using a schematic Hamiltonian that possesses a perturbed SU${}^{*}$(3) dynamical symmetry, the theory is applied for the calculation of the low-lying energy spectrum of the nucleus ${}^{192}$Os. The theoretical results obtained agree reasonably with the experimental data and show a very shallow triaxial minimum in the energy surface for the ground state in ${}^{192}$Os, suggesting that the proposed dynamical symmetry might be appropriate for the description of the collective properties of different nuclei, exhibiting triaxial features.

Study of triaxiality in Xe-Hg nuclei

The β and γ0 deformation parameters of even-even, Xe-Hg nuclei have been calculated in the frame work of rigid triaxial rotor model of Davydov and Filipov. The deformation parameters β and γ0 follow the smooth trajectories against the p-factor (p=NpNn/(Np + Nn)). The smooth variation between deformation parameter and p-factor is shown by dividing the Xe-Hg nuclei i.e. Z=50-82, N = 82-126 in to four quadrants (Q) viz. quadrant I and III for p-p and h-h bosons, and II, IV are h-p and p-h bosons respectively.

Properties of the 3/2−[521] band in the odd-N rare-earth nuclei

High-spin states in 161Er have been studied experimentally via the 150Nd(16O, 5n) reaction at a beam energy of 86 MeV. Three rotational bands built on the 5/2+[642], 3/2−[521], and 11/2−[505] configurations have been extended up to high-spin states, and particularly, the α = −1/2 branch of the ground state 3/2−[521] band has been revised significantly. It is found that signature inversion occurs in the 3/2−[521] band after the band crossing in 161Er. The systematics of the signature inversion associated with the 3/2−[521] configuration in the rare-earth region is discussed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and a triaxial deformation is proposed to the 3/2−[521] band.

The first candidate for chiral nuclei in the [formula omitted] mass region: 80Br

Excited states of 80Br have been investigated via the 76Ge(11B, α3n) and 76Ge(7Li, 3n) reactions and a new ΔI=1 band has been identified which resides ∼ 400 keV above the yrast band. Based on the experimental results and their comparison with the triaxial particle rotor model calculated ones, a chiral character of the two bands within the πg9/2⊗νg9/2 configuration is proposed, which provides the first evidence for chirality in the A∼80 region.

Crystal defects and related stress inY2O3thin films: Origin, modeling, and consequence on the stability of theC-type structure

We study the impact that the crystal defects have on the $C$-type structure of rare earth sesquioxide thin films grown by ion-beam sputtering, through the example of ${\mathrm{Y}}_{2}$O${}_{3}$. By monitoring the energy of the argon beam used in the sputter deposition process (between 600 and 1200 eV), we show that it is possible to control the microstructure (defects concentration, stress state and phase) in the oxide layer. Two main types of defects, ascribed to the ``atomic peening effect'', are evidenced by high-resolution transmission electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis experiments: anti-Frenkel pairs, leading to a disorder on the oxygen-vacancy network, and oxygen-vacancy dislocations loops, to accommodate the strong nonstoichiometry. From a macroscopic measurement of the residual stresses in the as-deposited and the annealed layers, through x-ray diffraction and the $\mathrm{sin}{}^{2}\ensuremath{\Psi}$ method, we have modeled the related stress state using an enhanced triaxial stress model. In the as-grown films, we evidence the coexistence of a biaxial and a hydrostatic stress, due to inclusions of atomic size defects. Quantitative information of the concentration and the nature of each type of defect (size effect) have also been determined, in good agreement with experiments. Interestingly, in the most energetic growth conditions corresponding to the highest degree of disorder on the oxygen-vacancy network and to the highest stress field in the film, we demonstrate that it is possible to stabilize an unexpected and metastable non equilibrium fluorite-like phase (X-type).

INTRINSIC SHAPE OF STAR-FORMING BzK GALAXIES ATz∼ 2 IN GOODS-N

We study structure of star-forming galaxies at z~2 in GOODS-N field selected as sBzK galaxies down to K_{AB} <24.0 mag. Among 1029 sBzK galaxies, 551 galaxies (54%) show a single component in ACS/F850LP image obtained with the Hubble Space Telescope; the rest show multiple components. We fit the single-component sBzK galaxies with the single S\'ersic profile using the ACS/F850LP image and find that a majority of them (64%) show S\'ersic index of n=0.5-2.5, indicating that they have a disk-like structure. The resulting effective radii typically range from 1.0 to 3.0 kpc in the rest-frame UV wavelength. After correcting the effective radii to those in the rest-frame optical wavelength, we find that the single-component sBzK galaxies locate in the region where the local and z~1 disk galaxies distribute in the stellar mass-size diagram, suggesting comparable surface stellar mass density between the sBzK and z~0-1 disk galaxies. All these properties suggest that the single-component sBzK galaxies are progenitors of the present-day disk galaxies. However, by studying their intrinsic shape through comparison between the observed distribution of apparent axial ratios and the distribution for triaxial models with axes (A>B>C), we find that the mean B/A ratio is 0.61^{+0.05}_{-0.08} and disk thickness C/A is 0.28^{+0.03}_{-0.04}. This indicates that the single-component sBzK galaxies at z~2 have a bar-like or oval shape rather than a round disk shape. The shape seems to resemble to a bar/oval structure that form through bar instability; if it is the case, the intrinsic shape may give us a clue to understand dynamical evolution of baryonic matter in a dark matter halo.

High-spin level structure ofRh115: Evolution of triaxiality in odd-even Rh isotopes

High-spin excited states in the neutron-rich nucleus $^{115}\mathrm{Rh}$ have been identified for the first time by studying prompt $\ensuremath{\gamma}$ rays from the spontaneous fission of $^{252}\mathrm{Cf}$ with the Gammasphere detector array. A new yrast band and a sideband are built in $^{115}\mathrm{Rh}$. This level scheme is proposed to be built on the $7/{2}^{+}$ ground state. The existence of a large signature splitting and an yrare band in $^{115}\mathrm{Rh}$ shows typical features of a triaxially deformed nucleus. The rigid triaxial rotor plus particle model is used to interpret the level structure of $^{115}\mathrm{Rh}$. The level energies, the $\ensuremath{\gamma}$ branching ratios, the large signature splitting in the yrast band, and the inverted signature splitting in the yrare band in $^{115}\mathrm{Rh}$ are reproduced very well. Strong $K$ mixing occurs in $^{115}\mathrm{Rh}$ at high spin.

Dark halos acting as chaos controllers in asymmetric triaxial galaxy models

We study the regular or chaotic character of orbits in a 3D dynamical model, describing a triaxial galaxy surrounded by a spherical dark halo component. Our numerical experiments suggest that the percentage of chaotic orbits decreases exponentially as the mass of the dark halo increases. A linear increase of the percentage of the chaotic orbits was observed as the scale length of the halo component increases. In order to distinguish between regular and chaotic motion, we chose to use the total angular momentum Ltot of the 3D orbits as a new indicator. Comparison with other, previously used, dynamical indicators, such as the Lyapunov Characteristic Exponent or the P(f) spectral method, shows that the Ltot indicator gives very fast and reliable results for characterizing the nature of orbits in galactic dynamical models.